This invention relates to an imaging element comprising a layer containing a random distribution of colored beads of one or more colors coated above one or more layers of silver halide emulsion grains, wherein the bead population comprises beads of at least one color in which at least 25% (based on projected area) of the beads of that color have an ECD less than 2 times the ECD of the silver halide grains either comprising said one layer or comprising the fastest layer of more than one layer.
The great majority of color photographs today are taken using chromogenic color film in which color-forming couplers, which may be incorporated in the film or present in the processing solution, form cyan, magenta and yellow dyes by reaction with oxidized developing agent which is formed where silver halide is developed in an imagewise pattern. Such films require a development process which is carefully controlled in respect of time and temperature, which is usually followed by a silver bleaching and a fixing step, and the whole process typically takes several minutes and needs complex equipment.
Color photography by exposing a black-and-white photographic emulsion through a color filter array which is an integral part of the film or plate on which the photographic emulsion is coated, has long been known to offer certain advantages of simplicity or convenience in color photography. Thus the Autochrome process, disclosed by the Lumiere brothers in 1906 (U.S. Pat. No. 822,532) exposed the emulsion through a randomly disposed layer of red, green and blue-colored potato starch grains, and the emulsion was reversal processed to give a positive image of the scene which appeared colored when viewed by light transmitted through the plate. The process allowed the formation of a colored photograph without the chemical complexity of later photographic methods.
The Dufaycolor process (initially the Dioptichrome plate, L.Dufay, 1909) used a regular array of red, green and blue dyed patches and lines printed on a gelatin layer in conjunction with a reversal-processed black-and-white emulsion system, which similarly gave a colored image of the scene when viewed by transmitted light.
Polavision (Edwin Land and the Polaroid Corporation, 1977) was a color movie system employing a rapid and convenient reversal processing method on a black-and-white emulsion system coated above an array of red, green and blue stripes, which gave a colored projected image. It was marketed as a still color transparency system called Polachrome in 1983.
These methods suffered a number of disadvantages. The images were best viewed by passing light through the processed film or plate, and the image quality was not sufficient to allow high quality prints to be prepared from them, due to the coarse nature of the Autochrome and Dufaycolor filter arrays, and the coarse nature of the positive silver image in the Polavision and Polacolor systems. The regular array patterns were complicated and expensive to manufacture. In addition, the films which used regular or repeating filter arrays were susceptible to color aliasing when used to photograph scenes with geometrically repeating features.
U.S. Pat. No. 4,971,869 discloses a film with a regular repeating filter array which claims to be less susceptible to aliasing problems. The film comprises a panchromatic photographic emulsion and a repetitive pattern of a unit of adjacent colored cells wherein at least one of the cells is of a subtractive primary color (e.g. yellow, magenta or cyan) or is of a pastel color. Scene information can be extracted from the developed film by opto-electronic scanning methods.
U.S. Pat. No. 6,117,627 discloses a light sensitive material comprising a transparent support having thereon a silver halide emulsion layer and a randomly arranged color filter layer comprising colored resin particles. The material has layer arrangement limitations and results in increased fogging of the sensitized layer. The patent discloses the preparation of a color filter array using heat and pressure to form the color filter layer prior to application of the light sensitive layer to a support. Due to the necessary use of pressure and heat, it is not practical to use the teachings of this patent to prepare a film having a light sensitive layer between the color filter layer and the support. Attempting to apply the needed heat and pressure to bond the filter layer to the rest of the multilayer would damage the light sensitive layer. The patent also discloses exposing, processing and electro-optically scanning the resultant image in such a film and reconstructing the image by digital image processing.
Color photographic films which comprise a color filter array and a single image recording layer or layer pack have the advantage of rapid and convenient photographic processing, as the single image recording layer or layer pack can be processed rapidly without the problem of mismatching different color records if small variations occur in the process. A small change in extent of development for example will affect all color records equally. Exceptionally rapid processing is possible using simple negative black-and-white development, and if suitable developing agents are included in the coating, the photographic response can be remarkably robust or tolerant towards inadvertent variations in processing time or temperature.
Copending and commonly assigned U.S. Ser. No. 09/922,273, filed Aug. 3, 2001, the contents of which are incorporated herein by reference, discloses a color film comprising (1) a support layer, (2) a light sensitive layer, and (3) a water permeable color filter array (CFA) layer comprising a continuous phase transparent binder containing a random distribution of colored transparent beads, said beads comprising a water-immiscible synthetic polymer or copolymer.
An undesirable feature of the random color filter array in general is the introduction of noise into the imaging system due to the randomness of the array. For the purposes of illustration, consider the case of a system with three bead colors, red, green, and blue, although the ideas to be discussed hold independent of this specific embodiment. Define the average projected areal coverage of beads of each color is  less than r greater than ,  less than g greater than , and  less than b greater than  for red, green, and blue beads, respectively. If one considers a certain aperture size corresponding, for example, to the aperture size of a scanning device used to scan this film, then because of random fluctuations the actual areal coverages of the beads in this aperture region, r, g, and b, will not in general be exactly equal to the above average values. Rather, as the aperture is scanned over the array, the values of r, g, and b will fluctuate about the average values of  less than r greater than ,  less than g greater than , and  less than b greater than . It is desirable to minimize the magnitude of these fluctuations in areal coverage.
It is well-understood from basic statistical considerations that, for a given aperture size, the noise (i.e., the magnitude of these fluctuations) will decrease as the size of all of the beads, in toto, is made smaller. However, if the system contains beads with a distribution of sizes, it is not clear to what extent reducing the size of only a portion of the beads will reduce the noise. In particular, it is not clear to what extent reducing the size of only the beads of a certain color or colors will reduce the noise. This latter question is important because manufacturability issues, such as the ability to load dye into the beads, may set a lower limit on the size of one or more colors of the beads. While reducing the noise level is a goal, it is desirable to achieve that objective without causing undesirable effects on the imaging system as a whole because, if the beads become too small relative to the underlying emulsion grains, then it is expected that the quality of the color reproduction will be sacrificed (and the noise of the imaging system as a whole may even be increased).
Japanese published application 09-145,909 discloses the use of a silver halide material as a means of placing colored filter elements on a liquid crystal display. U.S. Pat. No. 5,998,109 discloses a light sensitive silver halide material containing at least three stripe-like or mosaic layers having different spectral transmission characteristics. This patent is unclear as to how the three layers are arranged. Moreover, this patent does not address the issue of controlling the noise level of the image information. It gives broad ranges of filter and grain sizes but does not address the importance of selecting the relative sizes on the resulting noise levels.
It is a problem to be solved to provide a silver halide emulsion film employing colored beads wherein the size of the beads is selected relative to the silver halide grain size so that the noise level is reduced.
The invention provides an imaging element comprising a single layer containing a random distribution of a colored bead population of one or more colors coated above one or more layers comprising light sensitive silver halide emulsion grains, wherein the population comprises beads of at least one color in which at least 25% (based on projected area) of the beads of that color have an ECD less than 2 times the ECD of the silver halide grains in said one emulsion layer or in the fastest emulsion layer in the case of more than one emulsion layer. The invention also provides an imaging process employing the imaging element.
Embodiments of the invention provide a silver halide emulsion film employing colored beads wherein the size of the beads is selected so that the noise level is reduced.